1. Field of the Invention
This invention relates to a semiconductor device composed of a plurality of circuit substrates stacked one on top of another, each circuit substrate provided with at least one circuit element. More particularly, this invention relates to a different-types-embedded semiconductor package (SBM (System Block Module)), such as an SiP (System in a Package) formed by squeezing a logic circuit and different types of semiconductor parts, including memory elements and analog elements, into a package.
2. Description of the Related Art
In recent years, an SBM composed of different types of semiconductor parts stacked one on top of another in a single package has been developed. The SBM has attracted attention because it is available in a smaller-sized package than an existing MCM (multi-chip module) composed of a plurality of chips arranged two-dimensionally.
FIG. 6 shows an example of the configuration of a conventional SBM. In the figure, the configuration of an SBM is shown two-dimensionally, using a case where a memory controller circuit and a memory element are combined. As shown in FIG. 6, in the SBM, a first circuit substrate layer 1 and a second circuit substrate layer 2 are arranged three-dimensionally. Then, the peripheries of the first circuit substrate layer 1 and second circuit substrate layer 2 are sealed with a package 3. In this example, the first circuit substrate layer 1 has a memory controller circuit on it. The second circuit substrate layer 2 has a memory clement on it.
In the SBM, existing finished semiconductor parts, such as memory controller circuits or memory elements, are mounted as they are on individual circuit substrates. Then, circuit substrates on each of which a semiconductor part is mounted are stacked one on top of another. This makes it possible to squeeze the substrates into a smaller-sized package as described above. As compared with an ordinary memory-embedded package, the SBM can be developed in a shorter time, which helps reduce the cost. That is, in the case of existing memory-embedded packages, each time a product is developed, a logic circuit and other related circuits have to be designed. Therefore, the commercialization of the product requires a very long time and a lot of funds.
The SBM with the above configuration has the advantage of being capable of carrying out a comprehensive test of the entire system easily (in the normal operation test mode). However, it is difficult for the SBM to test the memory element independently. The reason is that, in a conventional SBM, the input and output signals of the memory controller circuit are connected with the input and output signals of the memory element in a complicated manner. Therefore, it is difficult to test the memory element directly without a help of the memory controller circuit.
A method of testing the memory element independently is as follows. For example, a special input pin connected to the memory element is provided separately from the input pin used for inputting an input signal to the SBM. Use of the special input pin different from the input pin connected to the memory controller circuit enables the input signal to be inputted directly to the memory element (see FIG. 6). This makes it possible to test only the memory element easily (a conventional single-unit test mode). However, when special input pins for testing memory elements independently are provided, the number of input and output pins of the SBM increases. This causes the problem of increasing the package size (impairing the advantage of the small package size).